The present invention relates to a magnetic recording medium which employs a CoP alloy as a magnetic film.
There have hitherto been proposed magnetic recording media in which a primary coat comprising Cr or the like is formed on a non-magnetic substrate such as plastics, for example, polyesters, polyamides, polyimides, or aluminum, and a magnetic film comprising a CoP alloy is then formed.
As for the primary coat of the magnetic film which is formed by the sputtering of a CoP alloy or a CoNiP alloy, for example Japanese Patent Laid-Open Publication No. 77024/1983 discloses the use of Al, Cr or Ti as the primary coat, and Japanese Patent Laid-Open Publication No. 77027/1983 discloses the use of a Cr alloy which contains 60% by weight or less of one of Mo, Ti, Fe, Co and Ni.
As for the magnetic film itself formed by the sputtering of the CoP alloy or the CoNiP alloy, it has also been reported that when a CoNiP teralloy or a CoNiPCr tetralloy are used as a magnetic material, the s/N ratio can be increased and the noise can be decreased in comparison with P-free alloys such as CoNi or CoNiCr (KUBOTA GIHO, No. 20, pp. 19-23 (April, 1988)).
Also, Japanese Patent Laid-Open Publication No. 116707/1983 discloses the magnetic films comprising CoP alloys or CoNiP alloys having a percentage composition of P in the range of 6-8% by weight.
On the other hand, magnetic films containing Pt such as a CoPt alloy or the like have also been applied to magnetic media such as magnetic disks or the like.
However, the magnetic recording media described in the aforementioned publications as well as other conventional magnetic recording media have a coercive force H.sub.c of at most about 1200 oersteds, and the heating of a non-magnetic base to 200.degree. C. or more or the addition of Pt in an amount of up to 15 at % to a Co alloy are required in order to obtain the coercive force H.sub.c of 1200 oersteds or more. If these requirements are satisfied, some of the non-magnetic bases are restricted by their heat-resistant temperature or the magnetic recording materials become expensive because of the use of Pt in a large amount, so that magnetic recording materials for practical use have not been proposed from the standpoint of their costs.
As described above, there was hitherto no such magnetic recording medium wherein a non-magnetic base requires heating to a temperature of less than 200.degree. C., retains coercive force H.sub.c of 1200 oersteds or more and has a low noise on regeneration even if Pt to be added to the Co alloy film is decreased to an amount of 10 at % or less from the standpoint of the cost. Recently, it is expected to supply such magnetic recording mediums with the improvement or low-gapping of a head of magnetic disks.